The present invention relates to an electrophotographic photoreceptor; an image forming method and an image forming apparatus and a process cartridge utilizing the same.
In recent years, an organic photoreceptor is widely utilized as an electrophotographic photoreceptor. An organic photoreceptor, in contrast to other photoreceptors, is provided with advantageous points of enabling such as easy development of materials corresponding to various types of exposure light sources from visible light to infrared light, selection of materials without environmental pollution, and lower manufacturing cost. However, disadvantages are problems of deterioration of electrostatic characteristics of a photoreceptor and generation of abrasion on the surface of the photoreceptor, at the time of making a large number of copies, due to poor mechanical strength and chemical durability.
That is, since the surface of a photoreceptor is directly applied with electrical and mechanical external forces by such as a charging device, a developing section, a transferring section and a cleaning section, resistance against them is required for said photoreceptor.
Specifically, there has been required improvement of resistance to generation of abrasions and flaws on the photoreceptor surface and to deterioration of the surface due to active oxygen such as ozone, and nitrogen oxide, which are generated at corona charging.
To solve the problems of mechanical and chemical durability such as described above, many organic photoreceptors employ an accumulated constitution comprising a charge generating layer and a charge transfer layer, the charge transfer layer at the surface layer being comprised of a uniform layer, which has high strength as well as minimum permeability of an active gas and provided with a layer thickness of not less than 20 μm.
However, since it is not advantageous for maintaining high image quality when a charge transfer layer is made to be too thick, heretofore, already proposed has been an organic photoreceptor, in which a charge transfer layer is made thinner to prevent diffusion of an electrostatic latent image, in such as JP-A No. 5-119503 (hereinafter, JP-A refers to Japanese Patent Publication Open to Public Inspection). However, these proposed organic photoreceptors still have not sufficiently answered the requirements of durability of a photoreceptor and higher quality images.
As a method to improve anti-abrasion characteristics of an organic photoreceptor, in addition to a protective layer utilizing curable silicone resin, there is described, in JP-A Nos. 56-117245, 63-91666 and 1-205171, that durability can be improved by incorporating silica particles in the outermost surface layer of a photoreceptor to increase mechanical strength of the photoreceptor surface. Further, in such as JP-A Nos. 57-176057 and 61-117558, and Patent literature 1, described is that a photoreceptor having higher durability is obtained by incorporating hydrophobic silica particles, which is comprised of the aforesaid silica particles having been subjected to a treatment by such as a silane coupling agent, in the outermost surface layer of a photoreceptor to increase mechanical strength of the photoreceptor as well as to provide a photoreceptor with lubricity.
However, in these abrasion resistance improvement techniques, there is observed a tendency of deterioration in image quality, particularly, in sharpness when repeated image formation is performed to provide many sheets of copied images.
Further, a method to incorporate an antioxidant in a charge transfer layer has been studies for many years (for example, refer to patent literature 2).
Further, there are many examples of constituting a charge transfer layer with plural layers to increase physical strength of the charge transfer layer surface while keeping high charging characteristics as a photoreceptor (for example, refer to patent literature 3).
These were effective to improve characteristics of an organic photoreceptor, however, nowadays, the required level of capability improvement with respect to an organic photoreceptor is high and they cannot be said satisfactory in this sense.
On the other hand, for image formation of a digital image having a high resolution, it is necessary to precisely develop a digital dot latent image by making toner adhere on an electrostatic latent image formed on an organic photoreceptor. That is, to form a toner image which faithfully reproduces an electrostatic latent image without spattering of toner on an organic photoreceptor, it is important to make foreign materials not adhere on the organic photoreceptor surface and to make the surface be not roughened even with repeated use. [Patent Literature 1] JP-A No. 3-155558 (hereinafter, JP-A refers to Japanese Patent Publication Open to Public Inspection)
[Patent Literature 2] JP-A No. 1-106066 [Patent Literature 3] JP-A No. 2-160247
This invention has been made in view of the foregoing problems.
Particularly, by employing all of the above-described improvement techniques, an effect accumulating these techniques cannot necessarily be obtained and even they may cancel functions each other by combination use of these techniques, as a result, it has been proved how to combine these techniques is a big problem. Therefore, the inventors of this invention have studied combinations of various durability improvement techniques, which are suitable to provide an electrophotographic photoreceptor which maintains high sensitivity and mechanical strength even in a long term use as well as gives stable charging potential, without image flows and deterioration against gas.